Cathode



M. C. PEASE March 21, 1950 CATHODE Filed Aug. 20, 1948 0. m M a m W M [P A Q d in s r m Patented Mar. 21, 1950 CATHODE Marshall 0. Pcase, Needham, Mass, assignor to Sylvania Electric Products Inc., Salem, Mass, a corporation of Massachusetts Application August 20, 1948, Serial No. 45,363

This invention relates to cathode construction and particularly to an improved cathode for use in a magnetron.

It has been found in practice that the efliciency and output capacity of a magnetron is substantially adversely affected by stray electrons. It becomes desirable therefore to control and utilize a high percentage of its electron emission and confine the electrons to the space within the tube in which they will perform the useful work of the tube.

It is an object of the invention to provide a cathode which exercises more complete control over its electron emission.

A further object of the invention is to provide a cathode having an improved structure operable to prevent excessive endwise movement of electrons during tube operation.

A further object of the invention is to provide a cathode having operating characteristics which contribute to extremely stable operation of the tube in which it is used.

Other objects and features of the invention will more fully appear from the following description and will be particularly pointed out in the claims.

The illustrative embodiment of the invention may be described briefly as follows. The cathode is of the indirect heater type having a heater element mounted in a hollow cylindrical cathode body member, the heater and cathode body having suitable electrical connections reaching to the outside of the tube. The body portion is provided with a suitable electron-emissive material on its outer surface. The electron-emissive material is confined to the working portion of the cathode which in the type of cathode shown is that portion adjacent the portion of the tube anode sections between which the oscillating field exists.

Without special means it is not possible to confine electron movements to a desired area. Various means have been used to prevent the path of electrons from invading areas where their presence will lower the efiiciency of the tube. Partial control of this electron spread has been achieved in various ways. The present invention provides a combination of electron controlling elements including flange-like bafiles and axially extending vanes associated with the baifies which substantially eliminate endwise escape of electrons out of the designated oscillating field.

Forces acting upon the electrons create a great deal of turbulence at and beyond the ends of the working portion of the cathode. These forces 4 Claims. (01. 250-275.)

have a component causing axial movement there-- of which if permitted to function cause inefiiciency and loss of power output or may cause failure of the tube to oscillate. The present invention prevents this turbulence and thus prevents most of the electrons from escaping into areas where they will impair tube operation.-

To provide a better understanding of the invention a specific embodiment thereof will now be described and illustrated in the accompanyin drawings in which:

Figure l is a cross section of a magnetron embodying the invention.

Figure 2 is a perspective view of a cathode detached from a tube showing the details of the invention as embodied therein.

Figure 3 is a longitudinal sectional view of the cathode.

Figure 4 is a cross section through the cathode taken on line 44.

The cathode shown is cylndrical inform and has a hollow metallic body member I which is secured within the envelope 2 of the tube in which it is used. The central portion of the cathode is coated with an activating material 3 such as is commonly used to provide a zone of high electron emission.

The emissive material is applied to the cathode at the portion of its bodyadjacent the resonating portion of anode sections 4 of the tube. The active material 3 supplies the electron flow to support the tube output. I

The anode sections 4 constitute. the resonator system and are shown as of the interdigital type but may be of any suitable type. The cathode is mounted in position within the tube envelope 2 to supply electrons to the resonator system of the tube. The members 4 have the general contour of a hollow cylinder and the cathode is placed upon the axis thereof within the cylinder.

As shown the cathode is supported upon a rod 5 extendin axially therethrough. The rod is mechanically connected to the cathode by insulating collars 6 secured in the ends of the cathode. The rod itself is secured to the envelope 2 by short rod sections the ends of which are anchored in the glass. One rod 1 is led through the glass and serves as the cathode lead of the tube.

A heater coil 8 is situated within the cathode. The heater surrounds but is spaced from the rod 5. One end of the coil is connected to the lead I while its other end is led out through a hole in the collar 6 and is welded to a lead 9 fused through the envelope 2. Power for the heater is supplied through the leads I and 9.

The emissive material 3 extends along the cathode body I for a distance substantially equal to the axial length of the resonating portion of the anodes. A pair of intercepting flanges of annular baflles II! are formed integrally upon the metallic cathode body and are spaced from the ends of the active coating 3. In addition to the baflies III, a plurality of. vanes I l are also provided which coact with the members I!) to prevent escape of electrons into the space beyond the resonator elements.

The vanes H extend axially along the cathode body from the baffles 10 toward the edge of coating 3 and are desirably substantially the same height as that of the baiiles Ill. Two such vanes are provided at each end of the active material 3.

The vanes H are placed at the nodal planes of radio frequency voltage of the resonator system to avoid disturbing the normal operation of the tube. In the present form of the invention the vanes are thus spaced peripherally 180 from each other. In a diiferent mode of operation of the tube it may be found more efiective to provide more than the one pair of vanes i i.

In the operation of such tubes the alternating magnetic field set up thereby causes electrons on one side of the nodal plane to be accelerated axially in one direction and on the other side to be accelerated in the opposite direction. As a result of this action a substantial tendency exists for electrons to reach the space beyond the fingers of the resonator anodes. If a substantial amount of electrons do reach this area the efiiciency of the tube is lowered.

'The combined efiect of the baffles Ill and the vanes H act to trap the electrons and prevent their axially outward travel thus increasing the tube output capacity, its efiiciency and stability of operation.

What I claim is:

1. A cathode comprising an elongated metallic body member, a coating of electron emissive material on a portion of said body member, annular metallic flange-like baflles extending around said body member and spaced from the ends of said coating, said baiiles being substantially larger than the transverse dimension of the body member, and vanes on the cathode disposed axially thereof and extending from each baflle toward the ends of the coating whereby outward axial movement of the electrons beyond the baiiies is prevented.

2. A cathode comprising an elongated metallic body, electron emissive material covering a. portion of the length of said body, external flangelike metallic baiiies extending around said body and projecting outward therefrom, said bafiles being spaced from the ends of said coated portion of the body and at least one pair of substantially flat vanes extending along said body from said baflies toward the ends of the coated portion of the body and situated in a longitudinal central plane through said body.

3. A cathode comprising a hollow cylindrical metallic body member, a coating of electron emissive material covering a zone of said body member, annular metallic baflies surrounding and pro jecting a substantial distance outward from said body member, said baflles being spaced from each end of said emissive coating, a pair of substantially fiat vanes at each end of said coating situated 180 apart upon the periphery of said body member and extending lengthwise thereof from said bafiies toward the ends of said emissive coating, and heater means within said body member.

4. A magnetron device having a pair of reso nating anode portions and an envelope for enclosing the tube elements, a cathode secured in said envelope comprising a body portion, an electron emissive coating covering a zone of said body portion, annular baiiies extending outward from the periphery of said body portion and spaced from the ends of said emissive coating, and at least one pair of substantially fiat vanes on said body portion and extending from said baiiies to ward the ends of said emissive coating, said vanes being situated in the nodal planes of radio frequency voltage of said resonating anodes.

MARSHALL C. PEASE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,889,087 Crowley et al Nov. 29, 1932 1,989,819 Parrott Feb. 5, 1935 2,170,410 Imboden Aug. 22, 1939 2,448,573 Blazier et a1 Sept. '7, 1948 2,460,119 Blewett et al Jan. 25, 1949 2,462,869 Kather Mar. 1, 1949 2,466,922 Wax Apr. 12, 1949 OTHER REFERENCES Magnetron Cathodes, Martin A. Pomeranta, Proceedings of I. R. E. and Waves and Electrons, V01. 34, NO. 11, NOV. 1946. 

